This invention relates to ceramic coatings, and more particularly, it relates to ceramic coatings that are in-situ thermally oxidized to improve their resistance to molten metal, such as molten aluminum.
Non-metallic barrier coatings are applied to metallic substrata for the purpose of protecting the substrata from chemical reaction. Such protection depends on the contiguity of the coating for protection. Discontinuities in the coating can permit the transport of chemical species or agents to the underlying substrate surface where chemical reactions may occur and result in failure of the substrate. Such discontinuities include porosity within the coating and cracks, both pre-existing and those that develop in-service.
Heaters used for molten aluminum are usually enclosed in ceramic tubes. Such electric heaters are very expensive and are very inefficient in transferring heat to the melt because of the air gap between the heater and the tube. Also, such electric heaters have very low thermal conductivity values that are characteristic of ceramic materials. In addition, the ceramic tube is fragile and subject to cracking. Thus, there is a great need for an improved ceramic coatings suitable for use with heaters for molten aluminum, for example, having improved resistance to attack by the molten metal and which is efficient in transferring heat to the melt. The present invention provides such ceramic coating.